well you’ve gotta love ace archives, there’s actually still people using it ;)
i received one today and wenn trying to unace in my linux i get (with t as parameter to verify the archive):
munzli@freddy:~$ unace t archive.ace
UNACE v1.2 public version

Processing archive: archive.ace

Authenticity Verification:
created on 31.3.2002 by Laudahn

thefirstfile.txt
 Analyzing
File compressed with unknown method. Decompression not possible.

Error occurred

well after searching around i found out that there is a nonfree version of unace. how handy. it’s located in the multiverse repository of gutsy and can be installed with:
sudo apt-get install unace-nonfree

now you’ve got the unace version that will decompress my archive and another version named “unace-free”. i’m not sure why they named it the other Moneygram fees way around in the repos, but it works…